This application is a Continuation of International Application No. PCT/JP02/00562, filed Jan. 25, 2002.
The present invention relates to a polyester resin poly-condensed in the presence of an antimony compound which is to be used for molding of e.g. bottles, films, sheets and fibers, and a process for its production. More particularly, it relates to a polyester resin having the elution of antimony suppressed during the contact with water, solvent, etc., in a posttreatment step after the polycondensation, in a dying step after processed into polyester fibers and at the time of filling a content as used as a polyester container, etc.
Heretofore, a polyester resin such as a polyethylene terephthalate resin has been widely used as various packaging materials such as containers or films, or as fibers, etc., since it is excellent in mechanical strength, chemical stability, gas barrier property, hygienics, etc., and is relatively inexpensive and light in weight.
Such a polyester resin is produced mainly by using an antimony compound as a polycondensation catalyst. However, there has been concern about a problem such that the antimony compound or metal antimony remaining in the resin may elute, for example, in a step of being contacted with water for e.g. cooling after the polycondensation or in a step of being contacted with a solvent for e.g. dying after being processed into fibers, thus causing environmental pollution. Further, there has been concern about a possibility that in use as a packaging material for e.g. a container, it will elute from the container, for example, in a step of being contacted with hot water for e.g. heat sterilizing filling. Accordingly, various polyester resins have been proposed which are produced, for example, by using a titanium compound as a polycondensation catalyst instead of the antimony compound or using a titanium compound in combination therewith. However, there has been a problem such that the color tone of the polyester resin deteriorates, acetaldehyde, diethylene glycol, etc. will form, whereby the amount of such by-products in the polyester resin increases, or elution of antimony from the polyester resin cannot adequately be suppressed.
Meanwhile, when a polyester resin or the like is used for a hollow container for a beverage, it may be used, for example, for a non-carbonated beverage such as mineral water, tea or juice, or for a carbonated beverage. Further, irrespective of the non-carbonated or carbonated beverage, an unheated aseptic filling method and a heat sterilization filling method are available as methods for filling the beverage.
A conventional polyester resin obtainable by using an antimony compound as a catalyst has a high crystallization rate, whereby the transparency tends to be poor. Accordingly, especially when it is used for a hollow container for a non-carbonated beverage, it is common to suppress the crystallization rate to a proper level by copolymerizing e.g. diethylene glycol-isophthalic acid in a small amount and usually setting the molecular weight (usually represented by the intrinsic viscosity) of the resin to be relatively high, in order to form a container such as a bottle excellent in transparency. However, since a copolymer component is incorporated, there is a problem such that oriented crystallization will not adequately proceed at the time of molding, whereby it tends to be difficult to obtain a molded product having sufficient heat resistance and strength efficiently, and when formed into a molded product, the amount of by-products such as acetaldehyde contained in the molded product tends to increase. If the molecular weight is further increased, there has been a problem such that the productivity of the resin and the productivity in the molding tend to deteriorate, or the amount of by-products such as acetaldehyde tends to further increase.
Further, with a conventional polyester resin obtainable by using an antimony compound as a catalyst, the crystallization rate is high, and accordingly, it is common to carry out copolymerization of a corresponding amount of diethylene glycol as mentioned above, whereby the transparency when formed into a. container may be improved, but in a case where it is used as a bottle particularly for a carbonated beverage, which is transported in a state where a stress is exerted by the inner pressure of the contained beverage, there has been a problem that cracks are likely to form by external factors such as the environmental temperature, chemical agents or solvents.
For the purpose of e.g. imparting environmental stress cracking resistance to a bottle for a carbonated beverage, a method of copolymerizing a polyfunctional compound component (e.g. JP-A-5-84808) or a method of applying anneal treatment to a bottle (e.g. JP-A-6-297550) has, for example, been proposed. However, such methods are not necessarily satisfactory from the viewpoint of the thermal stability during the production of a bottle, the transparency as a bottle or the productivity of the bottle.
Further, with a conventional polyester resin obtainable by using an antimony compound as a catalyst, the crystallization rate is so high that when a bottle obtained by molding it, is used particularly for heat sterilization filling, there has been a problem that deterioration of the transparency of a preform by heat treatment before blowing at the time of molding a bottle, tends to be remarkable. Accordingly, there have been many proposals from the viewpoint of the polycondensation catalyst, such as a method of using a titanium compound or a germanium compound, and further a magnesium compound and a phosphorus compound, in combination with the antimony compound, as a polycondensation catalyst. However, according to the study by the present inventors, it has been found that although in each proposal, the effect of lowering the crystallization rate is observed, there has been a problem that the above-mentioned heat treatment at the time of molding a bottle, takes time and there will be a difference between local crystallization rates, for example, between inside and outside of the mouth stopper portion, whereby the dimensional precision at the mouth stopper portion cannot be stabilized.
Further, with a conventional polyester resin obtainable by using an antimony compound as a catalyst, the crystallization rate is so high that there has been a problem that at the time of molding a bottle, in the injection molding of a preform, it is necessary to set the molding temperature at a high level for melting and plasticizing, followed by injection into a mold and by quenching in order to maintain the transparency, and the molding temperature is obliged to be high, consequently, by-products such as acetaldehyde, cyclic low molecular weight products, etc. will form in the resin after the molding, and such acetaldehyde may adversely affect the taste of the content when used as a bottle, or such cyclic low molecular weight products tend to contaminate the blow molding mold, whereby for the cleaning of the mold, the productivity will substantially be reduced.
Further, in order to solve the above-mentioned various problems, various proposals have been made for a process for producing a polyester resin wherein the amount of the antimony is reduced, and a titanium compound or a germanium compound, and further a magnesium compound and a phosphorus compound or the like are used in combination. However, by any one of conventional methods, it is difficult to sufficiently suppress elution of antimony, and there has been a problem that the above-mentioned other various problems cannot be adequately solved, or the polymerizability deteriorates, whereby the productivity of the polyester resin tends to be poor.
For example, JP-A-9-87374 discloses a process for producing a thermoplastic polyester, characterized in that in the production of a thermoplastic polyester resin comprising a dicarboxylic acid component and an alkylene glycol component, a mixture of an antimony compound and a titanium compound, and at least one compound selected from alkali metal compounds and alkaline earth metal compounds, are used as a polycondensation catalyst.
JP-A-2000-128964 discloses a polyester resin produced by using an antimony compound as a catalyst and containing ethylene terephthalate as the main repeating unit, which is characterized in that the haze of a molded product having a thickness of 4 mm molded from this resin at a temperature of 290xc2x0 C., is not more than 3.0%, and the haze of a molded product having a thickness of 5 mm is not more than 15.0%.
Japanese Patent No. 03081104 discloses a polyester for forming a film comprising an aromatic dicarboxylic acid as the main acid component and an aliphatic glycol as the main glycol component, which is characterized in that the content of metal-containing precipitated particles by a catalyst used at the time of synthesizing the polyester, is not more than 0.01 wt % (based on the polyester), and the catalyst comprises a titanium compound or a titanium compound and an antimony compound, and the amounts of these metal elements satisfy the specific ranges. JP-A-2000-219726, JP-A-2000-219730, JP-A-2000-226444, JP-A-2000-226445, JP-A-2000-226446 and JP-A-2000-226500 disclose polyester resins containing Sb and Ti or/and Ge as catalysts, and having densities and density-increasing rates within specific ranges.
However, according to the study by the present inventors, elution of antimony is not adequately suppressed, and the polymerizability and the productivity of the polyester resin are poor.
The present invention has been made in view of the above-described prior art, and it is an object of the present invention to provide a polyester resin poly-condensed in the presence of an antimony compound and having elution of antimony suppressed, and a process for producing a polyester resin, whereby such a polyester resin can be obtained with good polymerizability and productivity.
The present invention has been made to accomplish the above object. Namely, the present invention relates to a polyester resin (hereinafter referred to as polyester ({circle around (1)})) produced by polycondensing a dicarboxylic acid component containing an aromatic dicarboxylic acid or its ester-forming derivative as the main component and a diol component containing ethylene glycol as the main component in the presence of at least an antimony compound and a phosphorus compound, via an esterification reaction or an ester exchange reaction, which is characterized in that the amount of antimony eluted when immersed in hot water of 95xc2x0 C. for 60 minutes in the form of particles having a number average particle weight of 24 mg, is not more than 1 xcexcg per 1 g of the polyester resin, as antimony atoms (Sb).
By such present invention, elution of antimony can be suppressed, and a polyester resin having a good color tone and having formation of by-products suppressed, can be provided.
One of preferred embodiments of the present invention is a polyester resin (hereinafter referred to as polyester {circle around (2)}) which is polyester {circle around (1)} wherein the ethylene glycol component is at least 96 mol % of the total glycol component, the diethylene glycol component is not more than 2.5 mol % of the total glycol component, the terephthalic acid component is at least 98.5 mol % of the total acid component, the intrinsic viscosity IV is from 0.65 to 1.0 dl/g, and the temperature-lowering crystallization temperature Tc2 is from 150 to 200xc2x0 C. According to this embodiment, even if the copolymerized amount is particularly small and the intrinsic viscosity is low, the crystallization rate is low, whereby when formed into a container such as a bottle, it is possible to obtain a container having excellent transparency, heat resistance and strength at high productivity, such being particularly suitable for a hollow container for a non-carbonized beverage such as mineral water, tea or juice.
Another preferred embodiment of the present invention is a polyester resin (hereinafter referred to as polyester {circle around (3)}) which is polyester {circle around (1)} and which contains an ethylene terephthalate unit as the main repeating constituting unit and is characterized by satisfying the following characteristics (1), (2) and (3):
(1) after formed into a molded product, the temperature-rising crystallization temperature (Tc1) is at least 155xc2x0 C., and the temperature-lowering crystallization temperature (Tc2) is at most 180xc2x0 C. or not observed,
(2) the difference (xcex94AA=AAsxe2x88x92AAo) between the acetaldehyde content (AAs; ppm) in a molded product after injection molding at 280xc2x0 C. and the acetaldehyde content (AAo; ppm) before the injection molding, is not more than 15 ppm, and
(3) when an injection-molded sheet having a thickness of 1 mm is immersed in a 0.2 wt % sodium hydroxide aqueous solution at 25xc2x0 C. in such a state that it is fixed along the outer circumference of a cylinder having a diameter of 32mm, the environmental stress rupture time is at least 10 minutes.
According to this embodiment, particularly, the transparency, strength, taste deterioration resistance of e.g. the contained beverage and environmental stress cracking resistance are good, such being particularly suitable for a bottle for a carbonated beverage.
Another preferred embodiment of the present invention is a polyester resin (hereinafter referred to as polyester {circle around (4)}) which is polyester {circle around (2)} or {circle around (3)} and which is characterized in that it contains a polyolefin resin or a polyamide resin in an amount of from 0.0001 to 1000 ppm, and after formed into a molded product, the temperature-rising crystallization temperature (Tc1) is from 155 to 165xc2x0 C., and the temperature-lowering crystallization temperature (Tc2) is at most 180xc2x0 C. or not observed. This embodiment has a characteristic such that particularly when formed into a hollow container, the transparency of the body portion will not deteriorate, and the crystallization rate at the mouth stopper portion is high, whereby the productivity of the hollow container is excellent, and the dimensional stability of the mouth stopper portion is excellent, and there will be no substantial deformation of the mouth stopper portion during hot filling, and it is suitable for a hollow container to be used by heat sterilization filling irrespective of a non-carbonated beverage or a carbonated beverage.
Another preferred embodiment of the present invention is a polyester resin (hereinafter referred to as polyester {circle around (5)}) which is polyester {circle around (1)} and which is characterized in that the haze in a thickness of 5 mm of a molded product after injection molding at 270xc2x0 C. is not more than 50%. According to this embodiment, even if the molding temperature is set to be lower than ever, molding is possible without impairing the transparency, whereby a molded product excellent also in transparency can be obtained while suppressing formation of acetaldehyde during the molding and suppressing contamination of the mold during the molding, and thus it is suitable for a hollow container irrespective of whether it is for a non-carbonated or carbonated beverage or whether it is for unheated aseptic filling or for heat sterilization filling.
Another preferred embodiment of the present invention is a polyester resin (hereinafter referred to as polyester {circle around (6)}) which is polyester {circle around (1)} and which is characterized in that the number of particles of at least 1 xcexcm in the interior of the resin is not more than 20 particles/0.01 mm3. According to this embodiment, the number of particles in the interior of the resin is particularly small, whereby at the time of forming fibers or films, there will be no substantial thread breakage or film rupture caused by the particles, or when formed into a film, there will be no substantial projections such as fish eyes on the surface, and thus, it is suitable for fibers and films.
Further, another gist of the present invention resides in a process for producing a polyester resin, which comprises polycondensing a dicarboxylic acid component containing an aromatic dicarboxylic acid or its ester-forming derivative as the main component and a diol component containing ethylene glycol as the main component, characterized in that a catalyst is added to the reaction system so that the following respective atoms derived from the catalyst will be contained in the following concentration ranges based on the obtainable polyester resin:
0 less than Txe2x89xa650 ppm
10xe2x89xa6Sbxe2x89xa6250 ppm
0.1xe2x89xa6Pxe2x89xa6200 ppm
6.0xe2x89xa6Sb/Pxe2x89xa630
(in the above formulae, T is the total concentration (ppm) of at least one type of atoms selected from the group consisting of titanium atoms, hafnium atoms and zirconium atoms in the resin, Sb is the concentration (ppm) of antimony atoms in the resin, and P is the concentration (ppm) of phosphorus atoms in the resin). According to this invention, it is possible to produce the polyester resin of the present invention having elution of antimony suppressed, with good polymerizability and productivity.